Surfaces of plastic eyeglass lenses and other optical lenses are generally subjected to treatments for enhancing their performance and functions. Examples of such treatments include a primer coating, a hard coating, a dyeing treatment, and an antireflection treatment.
Primer coatings give an optical lens the function of enhancing the adhesion between the optical lens substrate and a hard coating film, and improve impact resistance. For plastic eyeglass lenses, techniques have widely been used in which a primer liquid is applied onto a surface of the plastic eyeglass lens and is then heated to cure the primer. An immersion method has mainly been used, conventionally, for this technique. In this immersion method, a plastic eyeglass lens is immersed in a primer liquid and allowed to stand while being held by a jig. The lens is then pulled out from the liquid to form a primer film.
Hard coatings give an optical lens many functions, such as enhancing the durability of an optical lens surface, the adhesion between the lens surface and a deposition film, and the stability of dyeing properties. For plastic eyeglass lenses, techniques have widely been used in which a hard coat liquid is applied onto a surface of a plastic eyeglass lens and is then heated to cure the hard coat liquid. An immersion method and an spin coating method have mainly been used for this technique, conventionally. In the immersion method, a plastic eyeglass lens is immersed in a hard coat liquid and allowed to stand while being held by a jig, and is then pulled out from the liquid to form a hard coat film. In the spin coating method, a hard coat liquid is discharged onto a surface of a plastic eyeglass lens and followed by rotating at a high speed. Thus, a hard coat film is formed.
A dyeing treatment is used particularly in manufacturing process of plastic eyeglass lenses for giving lenses fashionability. In this treatment, various colors are dyed, and an immersion method has conventionally been used. In the immersion method, a plastic eyeglass lens is immersed in hot water in which dye particles are dispersed with a surfactant and is then pulled up.
An antireflection treatment is used to prevent reflection at optical lens surfaces. Surface reflection reduces the transmittance of optical systems and increases light not involved in image formation, thus degrading image contrast. An antireflection treatment therefore, provides wearers with good visibility. Antireflection films have conventionally been formed in a single layer or a multilayer by vacuum deposition. A curable liquid having antireflection characteristics has recently been devised.
Application methods such as ink jetting or spraying have been devised for coating techniques in which a treatment liquid is applied onto only a desired region of optical lenses. In ink jetting and spraying methods, droplets of a treatment liquid are discharged from a small nozzle. An apparatus using ink jetting or spraying is reduced in size and can apply a treatment liquid at a low electric power. In addition, the liquid can be used with a high efficiency and production costs can be reduced. Furthermore, these methods are expected to reduce the amounts of used solvents and wastes, which promotes environmental protection.
Application, however, of the curable liquid having antireflection characteristics requires precise and uniform control of film thickness in order to ensure high performance. In an immersion method, the thickness of the coating film decreases at the upper side of the optical member and increases at the lower side due to gravity. Also, in the spin coating method, the thickness of a coating film decreases at the rotation center of the optical member and increases at the outer region due to centrifugal force.